The following U.S. Pat. Nos. 3,232,391, 3,384,205, 6,328,141 and 6,394,237 illustrate typical drum brakes wherein a first brake shoe and a second brake shoe are resiliently retained on a backing plate through hold down pin arrangements. In each of these drum brakes, the hold down pin arrangements allow the first and second brake shoes to move toward a drum during a brake application while at the same time allowing return springs to move the first and second brake shoes to a position of rest on completion of a brake application. This type of drum brake is often used as a parking or emergency brake as disclosed in U.S. patent application Ser. No. 10/195,821 filed Jul. 15, 2002. When used as a parking and emergency brake, the use is limited, as it has been estimated that during the life of a vehicle less than twenty-five percent of the operators of a vehicle will use the emergency or parking brake on a regular basis. With such limited use even though this type of drum brake functions in an adequate manner there is a continual effort to simplicity the structure such as provided by the present invention.
A primary object of the present invention is to provide a drum brake wherein a single resilient member functions to both axially and linearly retain first and second brake shoes on a backing plate.
In more particular detail, the drum brake has first and second brake shoes that are positioned on a backing plate that is secured to the vehicle and radially aligned with a drum. The first and second brake shoes each have a first end that is aligned with an anchor post that extends from the backing plate and with an actuator member adjacent the anchor post while a second end of each of the first and second brake shoes are linked to each other by an adjuster mechanism. The first end of the first and second brake shoes is selectively spaced apart from each other by the actuator member. A resilient arrangement is connected to the first and second brake shoes for urging the first ends toward the anchor and the second ends toward the adjuster mechanism to define a rest position for the first and second brake shoes. In the rest position, there is a running clearance established between friction surfaces on the first and second brake shoes and a braking surface on the drum. An input member is connected to the actuator member for transmitting a force that moves the first and second brake shoes through the running clearance such that the friction surfaces contact the engagement surface of said drum to effect a brake application. The resilient member is characterized by first and second springs each of which have a first helical coil located between a first engagement section and a second engagement section, a second helical coil that extends from the first engagement section to a first end and a third helical coil that extends from the second engagement section to a second end. The first and second ends of each of the first and second springs are connected to the backing plate such that the first and second engagement sections respectively contact the webs of the first and second shoes and the second and third helical coils urge the first and second shoes toward the backing plate to retain the first and second shoes on the backing plate while the first helical coils urges the first and second shoes toward the actuator and the adjuster to define a rest position for the first and second brake shoes.
An advantage of this invention resides in the use of a single spring for a drum brake that both retains first and second brake shoes on a backing plate and urges the first and second brake shoes toward a position of rest in an absence of an input force being applied to effect a brake application.
A still further advantage of this invention resides in a spring having a return helical coil located between identical hold down helical coils wherein the hold down helical coils have a first spring force that is less than the return helical coil such that the spring is easier to move in a vertical direction than in a lateral direction.